Faced with its worst COVID-19 outbreak yet, China has been enforcing an expanding number of mass quarantines, strict lockdowns and border controls. The measures may yet work, but official data released Monday show they are exacting a grim toll on the world’s second-largest economy.

China’s economy expanded 4.8% in the first three months of this year compared with the same period last year. That pace was barely faster than the final three months of last year, and it also obscured a looming problem.

Much of that growth was recorded in January and February. Last month, economic activity slowed as Shenzhen, the technology hub in the south, and then Shanghai, the country’s biggest city, and other important industrial centers shut down. The lockdowns suspended assembly lines, grounded workers, trapped truck drivers and snarled ports. They confined hundreds of millions of consumers at home.